Various organic acids, such as citric acid, malic acid, lactic acid and the like, are produced by various techniques and are available in aqueous solutions from which it is desired to recover such acids in a purified and concentrated form.
Citric acid has been commercially removed from aqueous solutions thereof, such as fermentation beer, by the procedure of adding lime to form a precipitate of calcium citrate and then reacting the calcium citrate with aqueous sulfuric acid to form a citric acid solution and insoluble calcium sulfate. This procedure has the disadvantages of requiring expendable lime and sulfuric acid as well as disposal of calcium sulfate.
Liquid-liquid extraction procedures have also been proposed in the prior art. The use of long chain aliphatic amines dissolved in an appropriate solvent to extract organic acids is discussed in J. Soc. Chem. Ind. 67, 48 (1948). U.S. Pat. No. 2,539,472 discloses use of an amine-solvent mixture to extract citric acid, lactic acid, or tartaric acid. The resulting complex requires steam distillation to recover the citric acid, lactic acid or tartaric acid therefrom however. The use of a mixture of amines and hydrocarbons to extract citric acid, lactic acid or oxalic acid is disclosed in British Pat. No. 1,426,018. The recovery of citrate salts using an amine-organic solvent mixture for extraction of citric acid is also disclosed in U.S. Pat. No. 3,944,606. None of the above prior art discloses or suggests the combination of a water immiscible amine and a water immiscible organic acid to extract organic acids, such as citric acid.